Field of the Invention
This disclosure relates to an imaging apparatus configured to image an object to be examined by detecting a plurality of lights having different polarization components.
Description of the Related Art
In recent years, a tomographic image pickup using an interference by low coherence light (Optical Coherence Tomography: OCT) apparatus (hereinafter, referred to as OCT apparatus) has been put into practical use. With an OCT apparatus, a tomographic image of an object to be examined can be obtained at a high resolution and in a non-invasive manner. Therefore, the OCT apparatus is becoming an absolutely imperative apparatus for obtaining the tomographic image of an eyeground (fundus) of an eye to be examined specifically in ophthalmic field. In fields other than ophthalmology, an attempt is being made to take tomographic images of wall surfaces of a digestive organ, and a circulatory organ, by configuring the OCT apparatus to perform a tomographic observation of the skin, or as an endoscope or catheter.
In an ophthalmology OCT apparatus, an attempt is made to acquire not only a normal OCT image (also referred to as a luminance image) that represents the shape of the eyeground tissue, but also a function OCT image that represents optical characteristics and movements of the eyeground tissue. In particular, a polarization-sensitive OCT apparatus is developed as one of a function OCT apparatus, and is configured to acquire a signal by using a polarization parameter of light. The polarization-sensitive OCT apparatus is capable of drawing a nerve fiber layer having a birefringent property and a retina layer having a property of resolving polarization, so that research aiming at glaucoma or age-related macular degeneration is being advanced.
At this time, the polarization-sensitive OCT apparatus forms a polarization OCT image by using the polarization parameter (retardation and orientation), which is one of the optical characteristics of the eyeground tissue, so that discrimination and segmentation of the eyeground tissue are performed. Generally, the polarization-sensitive OCT apparatus includes an optical system which is capable of correcting the polarized state of a measurement light and a reference light of the OCT apparatus by using a wavelength plate (for example, ¼ wavelength plate or a ½ wavelength plate). The polarized state of light ejected from a light source is corrected into a desired polarized state. The polarized state of a measurement light with which a sample is irradiated into a desired polarized state, the polarized state of the measurement light with which the sample is irradiated is corrected into a desired polarized state, and the light corrected in polarization is used to split and detect the interference light thereof as two orthogonal linearly-polarized beams, whereby a polarization OCT image is generated (J. Biomed. Opt. 18(2), 026008 (Feb. 1, 2013), Teresa Torzichy et al. “Retinal polarization-sensitive optical coherence tomography at 1060 nm with 350 kHz A-scan rate using a Fourier domain mode locked laser”).